Heretofore, glass has been widely used as a material for containers for seasonings, food oil, liquors such as beer and sake, cooling beverages such as carbonated drinks and the like, cosmetics, detergents, etc. However, glass containers are relatively high in manufacturing cost, though they are excellent in gas barrier properties, and therefore usually they are recovered after use and recycled for re-use. The drawbacks inherently associated with the glass containers, however, were such that because of heaviness for their size, they increase in shipping cost and, moreover, they are liable to break and not convenient for handling.
In order to overcome such drawbacks as mentioned above, various plastic containers have come to be used in place of the glass containers. Various plastic materials are used for the plastic containers, according to the kind of items to be preserved therein and the purpose for which the preserved items are used. Of these plastic materials, polyethylene terephthalate is used as a material, because of its excellent gas barrier properties and transparency, for containers for seasonings, cooling beverages, cosmetics and detergents. In these plastic containers especially for beer or carbonated drinks where the most severity of gas barrier properties is required, it may be said that even polyethylene terephthalate is not sufficient to meet such severe requirement. When these containers requiring severe gas barrier properties are intended to be manufactured from polyethylene terephthalate, it was necessary to improve gas barrier properties of the resulting container by increasing said container in wall thickness.
In the attempt as mentioned above, however, there was such a problem that the manufacturing cost of thick-wall bottles formed from polyethylene terephthalate becomes higher than that of thin-wall bottles, because the amount of the polyethylene terephthalate necessary for forming the thick-wall bottles are large in comparison with thin-wall bottles.
Under such circumstances, there is an attempt to obtain bottles excellent in gas barrier properties and economical efficiency from polyethylene terephthalate by highly orienting the polyethylene terephthalate used therefor. Bottles made of highly oriented polyethylene terephthalate may be obtained by orienting thick-wall preforms. In this case, however, there is brought about such a problem that the thick-wall preforms are gradually cooled in the course of the preparation thereof, and consequently highly oriented bottles obtained from these preforms undergo clouding and eventually deteriorate in transparency.
Such problem as mentioned above, on one hand, can be solved by using preforms formed from polyethylene terephthalate high in intrinsic viscosity. However, the use of polyethylene terephthalate high in intrinsic viscosity involves another problem that such polyethylene terephthalate as having a high intrinsic viscosity is poor in stretchability or moldability and also expensive.
Japanese Patent L-O-P Publn. No. 64624/1984 discloses molded articles formed from polyalkylene isophthalate such as polyethylene isophthalate or copolymers thereof as packaging materials having good gas barrier characteristics against oxygen and carbondioxide gas. Japanese Patent L-O-P Publn. No. 67049/1984 discloses multi-layer packaging materials comprising a layer of polyalkylene isophthalate such as mentioned above or copolymers thereof and a layer of polyalkylene terephthalate such as polyethylene terephthalate or copolymers thereof, and molded articles such as bottles composed of such multi-layer packaging materials.
There is proposed a process in which polyethylene and polyethylene terephthalate are blended (Japanese Patent L-O-P Publn. No. 64658/1984).
Japanese Patent L-O-P Publn. No. 167817/1983 discloses copolyesters obtained by copolymerization of isophthalic acid as dicarboxylic acid, and ethylene glycol and 1,3-bis(2-hydroxyethoxy)benzene as a dihydroxy compound component.
Further, there has been made a proposal to manufacture bottles excellent in gas barrier properties by using polyethylene terephthalate resin compositions, prepared by mixing polyethylene terephthalate resins with other resins.
For example, in the specification of Japanese Patent Application No. 205739/1987 previously filed by the present applicant, there are proposed PET resin compositions having gas barrier properties capable of withstanding preservation and shipment of carbonated drinks, said resin compositions comprising a blend of PET resin and polyhydroxypolyether resin. The containers molded from the above-mentioned PET resin compositions are superior in gas barrier properties to containers made of conventional PET resins.
Furthermore, the present applicant proposes by way of Japanese Patent L-O-P Publn. No. 72051/1986 PET resin compositions excellent in transparency, said PET resin compositions being obtained by mixing PET resin with copolymerized polyester resins.
Including of course such proposals as referred to above, the researches in improving transparency and gas barrier properties of PET resin compositions have heretofore been directed to place importance on the constitution of PET resin composition, and no attention has been focused on the draw ratio to be employed at the time when blow molded articles such as containers are prepared by stretching PET resin preforms.